http2: use io.ReadFull

This fixes an issue where an earlier matcher does not sufficiently
populate the buffer, preventing HTTP2 from reading enough bytes on the
Read call.

cmux_test.go

@@ -15,6 +15,8 @@ import (
 	"sync/atomic"
 	"testing"
 	"time"
+
+	"golang.org/x/net/http2"
 )
 
 const (
@@ -229,6 +231,51 @@ func TestAny(t *testing.T) {
 	runTestHTTP1Client(t, l.Addr())
 }
 
+func TestHTTP2(t *testing.T) {
+	defer leakCheck(t)()
+	errCh := make(chan error)
+	defer func() {
+		select {
+		case err := <-errCh:
+			t.Fatal(err)
+		default:
+		}
+	}()
+	writer, reader := net.Pipe()
+	go func() {
+		if _, err := io.WriteString(writer, http2.ClientPreface); err != nil {
+			t.Fatal(err)
+		}
+		if err := writer.Close(); err != nil {
+			t.Fatal(err)
+		}
+	}()
+
+	l := newChanListener()
+	l.connCh <- reader
+	muxl := New(l)
+	// Register a bogus matcher that only reads one byte.
+	muxl.Match(func(r io.Reader) bool {
+		var b [1]byte
+		_, _ = r.Read(b[:])
+		return false
+	})
+	h2l := muxl.Match(HTTP2())
+	go safeServe(errCh, muxl)
+	close(l.connCh)
+	if muxedConn, err := h2l.Accept(); err != nil {
+		t.Fatal(err)
+	} else {
+		var b [len(http2.ClientPreface)]byte
+		if _, err := muxedConn.Read(b[:]); err != io.EOF {
+			t.Fatal(err)
+		}
+		if string(b[:]) != http2.ClientPreface {
+			t.Errorf("got unexpected read %s, expected %s", b, http2.ClientPreface)
+		}
+	}
+}
+
 func TestHTTPGoRPC(t *testing.T) {
 	defer leakCheck(t)()
 	errCh := make(chan error)

matchers.go

@@ -2,7 +2,6 @@ package cmux
 
 import (
 	"bufio"
-	"bytes"
 	"io"
 	"io/ioutil"
 	"net/http"
@@ -77,8 +76,6 @@ func parseRequestLine(line string) (method, uri, proto string, ok bool) {
 	return line[:s1], line[s1+1 : s2], line[s2+1:], true
 }
 
-var http2Preface = []byte(http2.ClientPreface)
-
 // HTTP2 parses the frame header of the first frame to detect whether the
 // connection is an HTTP2 connection.
 func HTTP2() Matcher {
@@ -102,14 +99,12 @@ func HTTP2HeaderField(name, value string) Matcher {
 }
 
 func hasHTTP2Preface(r io.Reader) bool {
-	b := make([]byte, len(http2Preface))
+	var b [len(http2.ClientPreface)]byte
-	n, err := r.Read(b)
+	if _, err := io.ReadFull(r, b[:]); err != nil {
-	if err != nil {
 		return false
 	}
 
-	b = b[:n]
+	return string(b[:]) == http2.ClientPreface
-	return bytes.Equal(b, http2Preface)
 }
 
 func matchHTTP1Field(r io.Reader, name, value string) (matched bool) {